This invention relates generally to prosthetic devices, and more particularly, is directed to an acetabular prosthetic hip joint assembly with universal adjustability.
Each hip joint in the human body includes an acetabulum or natural socket in the pelvis that receives the femoral head or ball, which is joined to the femur or thigh bone by a neck portion. As a result, a ball-and-socket joint is provided. In many instances, however, total hip joint replacement may be required. For example, due to various progressive deteriorative diseases, such as osteoarthritis, or abnormal stresses applied to the hip joint, the hip joint, and particularly the femur neck, may fail. In some cases, only the femoral head and neck require replacement, while in other cases, the acetabulum must also be replaced.
Various hip joint prostheses have been proposed. Generally, an acetabular shell component or cup is cemented or press fit into the acetabulum socket in the bone. A femoral member comprising an elongated stem, a neck and a head are mounted to the femur by cementing or press fitting the stem into the intramedullary canal of the femur. The femoral head is then received in a socket insert fixedly secured within the acetabular shell component to provide a ball-and-socket movement therein. Generally, however, the socket insert, once installed, cannot be removed without destroying the same.
An example of an arrangement in which the socket insert is adjustable, is disclosed and shown in U.S. Pat. No. 4,678,472 to Noiles. The present invention is particularly related to the arrangement in FIGS. 33 and 34 thereof. In order to lock the socket insert to the acetabular shell component, screws pass through external lugs of the socket insert and through holes in the acetabular shell component. A small wedge is provided between the socket insert and the acetabular shell component so that, as the screws are tightened, the wedge is forced inwardly by one of the screws to provide a friction fit between the socket insert and acetabular shell component.
However, due to the use of lugs on the outer peripheral surface of the socket insert, it is necessary to completely remove the screws in order to adjust the angular position of the socket insert in the acetabular shell component. This is cumbersome and burdensome, particularly during an operation on a person. Further, the use of such lugs provides only marginal locking retention and limits the adjustability of the socket insert with respect to the acetabular shell component to only a few angular orientations of the socket face. Often times, however, minute variations are required which could not be obtained with this arrangement. Still further, because of this arrangement in which the wedge is actually fit within the outer wall of the socket insert, the socket insert is formed in two parts, which makes assembly difficult during an operation.
U.S. Pat. No. 3,818,512 to Shersher discloses a hip joint assembly with a symmetrical socket insert held in place within the acetabular shell by means of a self-locking nut threadedly received in the acetabular shell. However, this device, by providing a symmetrical socket insert, is not concerned with the different angular orientations thereof.